Shear force sensors are used in a wide range of disciplines. For example, they are used as slip sensors in robotic arms, tactile feedback sensors in biomedical engineering or frictional force sensors between two adjacent structural elements in civil engineering.
Different types of shear force sensors are commonly available. Such sensors usually make use of magneto-resistive elements, capacitive elements or semiconductor elements to measure shear forces. In a magneto-resistive sensor, a displacement of an object attached to a magnetic material of the sensor causes a change in the magnetic field. This change in the magnetic field in turn causes a change of resistance of a resistive element in the sensor, which is proportional to the shear force.
In a capacitive sensor, a shear force exerted on the sensor causes the capacitance of a capacitor of the sensor to change. The change of capacitance is proportional to the shear force.
Silicon/semiconductor sensors belong to a new trend of shear sensors using microfabrication technology. This type of sensor make use of piezoresistive effect in silicon for detecting shear force.
All the shear sensors described above are sensitive to Electro-Magnetic Interference (EMI), giving rise to inaccurate shear force readings when EMI is present. Moreover, the maximum shear force that can be exerted on these sensors are in general less than 100 N, making them unsuitable to be used for measuring shear force in heavy structures which may exert a shear force larger than 100 N on the sensor.
Thus it is desirable to have a shear force sensor which is small in size, immune to external interference like EMI and is able to accurately measure even large forces exerted on the sensor.